In radio systems, for example in the mobile radio field, it is often desirable to use a common antenna to transmit and receive signals. The transmission signals and received signals may lie in different frequency bands. The antenna which is used must be suitable for transmitting and receiving both frequency bands. Suitable frequency filtering separates the transmission signals and received signals, ensuring on the one hand that the transmission signals are passed on from the transmitter only to the antenna (not in the direction of the receiver), and on the other hand that the received signals are passed on from the antenna only to the receiver.
A pair of radio frequency filters may be used for this purpose, both of which pass a specific frequency band, namely the respectively desired frequency band (band pass filters). However, it is also possible to use a pair of radio frequency filters which block a specific frequency band, namely the respectively undesired frequency band. These are referred to as bandstop filters. It is also possible to use a pair of radio frequency filters: a first filter passes frequencies below a frequency that is between the transmission band and the reception band, and blocks the bands above this (low-pass filter); and a second filter blocks frequencies below this frequency that is between the transmission band and the reception band, and passes frequencies above this. This is what is referred to as a high-pass filter. Further combinations of the stated filter types may be used.
U.S. Pat. No. 6,392,506 B2 discloses a duplex filter in which radio frequency filters are interconnected and in which the inner conductor of a common coaxial transmission/reception connecting socket is connected via two conductor loops to in each case one closest resonator chamber in the transmission and receiving filters. In this case, a vertically projecting inner conductor is provided internally in each resonator chamber, with the chamber wall which bounds the resonator chamber radially on the outside being used as an outer conductor. In the corresponding already known solution, the area which is enclosed by the wire loop including the current feedback path via the inner wall of the resonator cavity to the outer conductor of the connecting socket (inductance) determines the strength of the signal injection in the respective filter path. The input can be tuned by mechanical deformation or bending of the wire loop.
In the capacitive case, the inner conductor of the common transmission/receiving connecting socket is split into two conductor pieces, which each end in flat metal pieces. The strength of the signal input is governed by the size and shape of these metal surfaces, and by their distance from the inner conductor of the respective resonator (the capacitance resulting from this). The input can likewise be tuned by mechanical deformation or bending of these metal surfaces, and by changing the distance to the respective inner conductor of the resonator filter.
Both variants have the disadvantage that the tuning process can be carried out only by purely reproducible mechanical manipulations (bending or deformation), and that the tuning of the input to one filter path also influences the electrical behavior of the respective other filter path, and vice versa, so that the two input devices must generally be varied alternately two or more times during the tuning process.
This disadvantage is avoided according to FIGS. 3 and 4 in the prior publication U.S. Pat. No. 6,392,506 B2 which has been mentioned, in that there is now only one capacitive input from the inner conductor of a common connecting socket to one resonator which is additionally provided for the two filter paths and may be referred to as a so-called “central resonator”. This provides coupling in the conventional manner via openings in the separating walls to in each case one resonator in the transmission filter path and one resonator in the receiving filter path.
However, in this case as well, the central resonator which is acquired in addition to the resonators in the filter path requires additional space and also results in additional costs, even though it does not significantly contribute to the frequency selectivity of the filter paths.
The exemplary illustrative non-limiting implementations herein provide for the interconnection of radio frequency filters, in order to produce a frequency diplexer, in a better way than the generic prior art.
In a first variant according to the exemplary illustrative non-limiting implementation, the two radio frequency filter paths are interconnected by means of an inductive or capacitive input to one resonator in a pair of resonators which are strongly coupled to one another (interconnection resonator pair). This avoids the disadvantages explained in the prior art. This means that, in contrast to the prior art, there is no longer any need to carry out a tuning process at the two points between which there is an interaction.
Furthermore, the resonator pair which are strongly coupled to one another contribute to selection of the two filter paths, to be precise in a similar manner to that if one of the two resonators were in each case permanently associated with one of the filter paths. This avoids the central resonator which is required in the prior art, causes additional costs, and furthermore, also requires even more space.
The coupling between the interconnection resonator pair and the filter paths in the frequency diplexers can in this case be carried out differently, namely,
according to the exemplary illustrative non-limiting implementation, it is possible for the two filter paths, namely the filter path for the transmission signals and the filter path for the received signals, to be coupled to the second resonator in the resonator pair which are strongly coupled to one another, which is not used for the input; or
both filter paths can be connected to the first resonator in the strongly coupled resonator pair, which is also used for the input from the inner conductor of a coaxial radio connection.
Advantageous, space-saving geometric arrangements of the resonator chambers are possible for certain numbers of resonators, but perhaps not for other forms of interconnection. For the purposes of the exemplary illustrative non-limiting implementations, it is thus possible, for example, to provide a frequency diplexer with a total of six resonators, which are arranged in two rows of three each, and in which all three connecting sockets, for the transmitter, for the receiver and for a common port or a common connecting socket (a common transmitting/receiving connecting socket, for example) for connection of an antenna or for the input/output of a common signal path, are located on the same side of the housing. The exemplary illustrative non-limiting implementation makes it possible to provide symmetrical, compact overall geometries.
Furthermore, one preferred illustrative non-limiting implementation allows particularly strong coupling by considerably shortening the distance between the inner conductors of the relevant resonators.
The radio frequency diplexer according to the exemplary illustrative non-limiting implementation is preferably constructed such that at least one resonator, preferably two or more resonators, and preferably all of the resonators, has or have a coaxial configuration. The radio frequency diplexer can likewise be constructed with one or more or all of the resonators using dielectric resonators, for example ceramic resonators. Finally, however, it is likewise possible to construct the radio frequency diplexer such that at least one resonator, but preferably two or more resonators or even all of the resonators, users or use stripline technology. In other words, all methods imaginable may be used, in which it is possible to approximately implement the explained principles.